Shroud assembly

ABSTRACT

In a turbomachine, axial flow leakage of motive fluid between rotor blade tips and the inner circumference of the outer casing is sometimes prevented by utilizing an overlapping (labyrinth) seal and shroud assembly between the blade tips and the outer casing. Removal and assembly of the overlapping shroud seal in an annular, non-split outer casing is greatly facilitated by providing a plurality of shroud segments about the blade tip periphery and a radially outer clearance gap between the shroud segments and the outer casing whereby each shroud segment may be moved radially to unlap the seal and permit axial removal of the seal without disturbing rotor elements.

United States Patent [191 Huber Feb. 18, 1975 SHROUD ASSEMBLY [75]Inventor: Thomas R. Huber, Waterford, N.Y.

[73] Assignee: General Electric Company,

Schenectady, N.Y.

[22] Filed: Sept. 27, 1973 [21] Appl. No.: 401,455

[52] 11.8. C1 415/172 A, 277/54, 415/209 [51] int. Cl. FOld 5/20 [58]Field of Search 4'15/170 R, 171, 172 A, 415/173, 209; 277/54, 56

[56] References Cited UNITED STATES PATENTS 2,416,268 2/1947 Nagler415/171 2,956,733 10/1960 Stalker 415/170 R FOREIGN PATENTS ORAPPLICATIONS 200,055 11/1955 Australia 415/172 A 19,669 0/1908 GreatBritain 277/56 444,814 3/1936 Great Britain 277/56 PrimaryExaminerl-lenry F. Raduazo Attorney, Agent, or Firm-Erwin IF. Berrier,Jr.

[57] ABSTRACT In a turbomachine, axial flow leakage of motive fluidbetween rotor blade tips and the inner circumference of the outer casingis sometimes prevented by utilizing an overlapping (labyrinth) seal andshroud assembly between the blade tips and the outer casing. Removal andassembly of the overlapping shroud seal in an annular, non-split outercasing is greatly facilitated by providing a plurality of shroudsegments about the blade tip periphery and a radially outer clearancegap between the shroud segments and the outer casing whereby each shroudsegment may be moved radially to unlap the seal and permit axial]removal of the seal without disturbing rotor elements.

3 Claims, 2 Drawing Figures Simon!) ASSEMBLY BACKGROUND OF THE INVENTIONThis invention relates in general to turbomachines and more particularlyto a shroud assembly for a turbomachine of the type having a non-splitannular outer casing.

In a turbomachine, the rotor blades are surrounded at their peripheriesby a circumferential shroud assembly attached to the outer casing of theturbomachine. The rotor blade tip and the shroud assembly are closelyadjacent one another to form a seal which prevents axial leakage of themotive fluid between the blade tips and the outer casing. One type ofseal is the so-called labyrinth seal wherein radially extending bladeteeth overlap, in the axial direction, radially depending shroud teeththereby forming an axial seal.

In the prior art, the overlapping (labyrinth) seal was used exclusivelyin conjunction with a horizontally split outer casing comprising upperand lower casing halves including upper and lower shroud segments.Replacement of the upper segment was accomplished by removal of theupper casing half. Removal of the lower shroud segment required removalof the rotor, the entire process being costly and time-consuming. It hasalso now become desirable to employ an annular or non-split outercasing. The present invention describes a construction and method forremoving an overlapping (labyrinth) type seal and shroud assembly froman outer casing without disturbing the rotor elements.

It is therefore one object of the present invention to provide anoverlapping (labyrinth) seal for an annular, non-split outer casing.

It is another object of the present invention to provide a method forremoving a shroud assembly from an annular, non-split casing.

Other objects and advantages will become apparent from the followingdescription of one embodiment of the present invention, and the novelfeatures will be particularly pointed out hereinafter in the claims.

SUMMARY OF THE INVENTION In a turbomachine including a rotor axiallydisposed within a non'split, annular outer casing, said rotor includinga plurality of radially extending blades, each blade formed with a tipportion having at least one seal tooth and said outer casing includingan annular recess adjacent said blade tip portions, an improved shroudassembly as hereinafter described. The shroud assembly includes aplurality of arcuate shroud segments disposed in said outer casingannular recess; each shroud segment including a radially dependingshroud tooth which overlaps a respective blade tooth in the axialdirection forming a labyrinth seal therewith. The annual recess isformed with an annular stop for radially locating said shroud segmentsrelative to said blade tips. Moreover, a clearance gap remains betweenthe radially outward portion of each shroud segment and the radiallyinward surface of said outer casing annular recess for receiving aspacer plate which bears against each shroud segment. Fastening meansare provided for attaching each shroud segment to the outer casing. Inassembly and disassembly operations, the spacer plate may be removedfrom said clearance gap whereby each shroud segment may be movedradially and axially.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a cross section of aturbomachine (lower half removed) disclosing the details of the presentinvention.

FIG. 2 is an enlarged cross section of a turbine blade and shroudassembly showing details according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings,particularly to FIG. 1, a turbomachine portion 11 includes annular outercasings 13 which may be axially joined at circumferential flanges 13aand 13b. The annular casings may be nozzle casings, exhaust casings,etc., as is well known in the art. The present invention finds itsgreatest utility in an annular or non-split outer casing, that is, acasing having no horizontal joint for assembly and disassembly. However,it will become apparent that the present invention may be applied to ahorizontally split outer casing, if so desired.

A rotor 15 is axially disposed within the outer casing and may include ahigh pressure wheel 17 and also a low pressure wheel 19. Each wheelcontains radially extending blades 21 circumferentially mounted aboutthe respective rotor wheels, as is well known in the art.

FIG. 2, in conjunction with FIG. 1, shows a rotor blade 21 mountedwithin the outer casing 13. Each rotor blade includes a tip portioncomprising a plurality of seal teeth 23. The blade seal teeth aredisposed to extend radially. outward from the blade tip. The blade teethform one portion of an axially extending labyrinth seal 25.

The remaining portion of the labyrinth seal comprises an annular shroudassembly formed by a plurality of shroud segments 27 (only one shown)disposed radially outwardly of the blade seal teeth, and having radiallydepending shroud teeth 29 overlapping in the axial direction, the bladeseal teeth. Otherwise stated, the shroud seal teeth extend radiallyinwardly between the radially outwardly extending blade teeth to createan interference in the axial direction. Each shroud segment is arcuateand the seal teeth may take the form of a number of arcuate rows.

The shroud segments are disposed in an annular recess 31 formed in theouter casing. An annular stop means 33 extends axially into the annularrecess. The shroud segment is formed with a mating recess 35 which abutsthe stop means when. the shroud segment is properly seated into theannular recess. The mating recess 35 is elongated to permit radialmovement of the shroud segment in the casing annular recess when themating recess is proximate the stop means. Each shroud segment is alsoformed with an axial bore 41 therethrough whereas the outer casing alsoincludes an aligned bore 43. A fastener 45 is threaded through theshroud bore and into the outer casing bore for fastening the shroudsegment to the outer casing.

Each shroud segment includes a radially outward surface 49 which isspaced from a radially inward surface 51 of the outer casing therebydefining an arcuate clearance 53 for allowing radial displacement of theshroud during assembly and disassembly. After assembly of each shroud, aspacer plate 55 is inserted into the clearance 53 for positioning theshroud segment radially inwardly toward the blade tips.

Having described the construction of the present invention, theoperation is as follows. With an adjacent casing removed, individualshroud segments may be inserted into a non-split annular turbomachineouter casing to form a labyrinth seal, in the axial direction, withrotor blade seal teeth while the rotor is axially positioned within theouter casing. Each shroud segment is axially inserted within the outercasing annular recess 31 until contact is made between the shroudsegment and the rear wall of the annular recess defined by a dependingportion of the outer casing as shown. Each shroud segment is heldradially outward in the clearance 53 until the proper circumferentialposition as heretofore defined is achieved. Thereafter, each shroudsegment is moved radially inward until annular stop 33 is contacted andthe respective blade and shroud teeth are disposed in an axiallyoverlapping position. Fasteners 45 are then inserted into bores 41 and43 in the shroud segment and outer casing respectively. This assembly isthe reverse of the aforementioned procedure whereby the shroud segmentis moved radially outward to unlap the blade and shroud teeth and thenaxially removed. Thus, in an annular non-split outer casing shroudsegments may be assembled and removed without disturbing the rotorblades.

While a specific embodiment of the invention has been shown, it will beobvious to those skilled in the art that changes and modifications maybe made without departing from the invention. It is therefore intendedin the appended claims to cover all such changes and modifications thatfall within the true spirit and scope of the invention.

What is claimed is:

1. In a turbomachine, including a rotor axially disposed within aunitary outer casing, said rotor formed with a plurality of radiallyextending rotor blades, each blade having at least one radiallyextending seal tooth; and, said outer casing being formed with an openend annular recess circumferentially adjacent said rotor blades sealteeth; a shroud assembly comprising:

a plurality of shroud segments disposed in said open end annular recess;

at least one shroud seal tooth radially dependent from each shroudsegment and overlapping a blade seal tooth in the axial direction toform an axial seal therewith; and,

a clearance defined between a radially outer surface of each shroudsegment and a radially inner surface of said outer casing whereby eachshroud segment may be moved radially outward to unlap respective bladeand shroud teeth prior to axial removal from the outer casing;

an annular stop formed on said outer casing extending axially into saidannular recess; and,

a recess formed in each shroud segment for engaging a portion of saidannular stop.

2. The shroud assembly recited in claim 1 wherein said recess formed inthe shroud segment is elongated in the radial direction to allow radialpositioning of the shroud segment when the shroud segment recess isproximate to the annular stop.

3. In a turbomachine a rotor axially disposed within an annular,non-split outer casing, said rotor formed with a plurality of radiallyextending rotor blades, each blade having radially extending seal teeth,and, said outer casing having an open end annular recesscircumferentially adjacent said rotor blade seal teeth; a shroudassembly comprising:

a plurality of shroud segments disposed in said open end annular recess;each shroudsegment including a plurality of radially depending shroudseal teeth which overlap said radially extending blade seal teeth in theaxial direction forming an axial labyrinth seal therewith;

a clearance defined between a radially outer surface of each shroudsegment and a radially inner surface of said outer casing;

a spacer plate removably positioned in said clearance between eachshroud segment and the outer casing;

an annular stop formed on saidouter casing extending axially into saidannular recess;

a recess formed in each shroud segment for engaging a portion of saidannular stop; and,

fastening means for attaching each shroud segment to the outer casing.

1. In a turbomachine, including a rotor axially disposed within aunitary outer casing, said rotor formed with a plurality of radiallyextending rotor blades, each blade having at least one radiallyextending seal tooth; and, said outer casing being formed with an openend annular recess circumferentially adjacent said rotor blades sealteeth; a shroud assembly comprising: a plurality of shroud segmentsdisposed in said open end annular recess; at least one shroud seal toothradially dependent from each shroud segment and overlapping a blade sealtooth in the axial direction to form an axial seal therewith; and, aclearance defined between a radially outer surface of each shroudsegment and a radially inner surface of said outer casing whereby eachshroud segment may be moved radially outward to unlap respective bladeand shroud teeth prior to axial removal from the outer casing; anannular stop formed on said outer casing extending axially into saidannular recess; and, a recess formed in each shroud segment for engaginga portion of said annular stop.
 2. The shroud assembly recited in claim1 wherein said recess formed in the shroud segment is elongated in theradial direction to allow radial positioning of the shroud segment whenthe shroud segment recess is proximate to the annular stop.
 3. In aturbomachine a rotor axially disposed within an annular, non-split outercasing, said rotor formed with a plurality of radially extending rotorblades, each blade having radially extending seal teeth, and, said outercasing having an open end annular recess circumferentially adjacent saidrotor blade seal teeth; a shroud assembly comprising: a plurality ofshroud segments disposed in said open end annular recess; each shroudsegment including a plurality of radially depending shroud seal teethwhich overlap said radially extending blade seal teeth in the axialdirection forming an axial labyrinth seal therewith; a clearance definedbetween a radially outer surface of each shroud segment and a radiallyinner surface of said outer casing; a spacer plate removably positionedin said clearance between each shroud segment and the outer casing; anannular stop formed on said outer casing extending axially into saidannular recess; a recess formed in each shroud segment for engaging aportion of said annular stop; and, fastening means for attaching eachshroud segment to the outer casing.